diagnostics: convert HTML output test plugin to 'experimental-html' sink [PR116792]

diagnostics: convert HTML output test plugin to 'experimental-html' sink [PR116792]

In r15-3752-g48261bd26df624 I added a test plugin that overrode the
regular output, instead emitting diagnostics in crude HTML form.

In r15-4760-g0b73e9382ab51c I added support for multiple kinds of
diagnostic output simultaneously, adding
 -fdiagnostics-add-output=DIAGNOSTICS-OUTPUT-SPEC
 -fdiagnostics-set-output=DIAGNOSTICS-OUTPUT-SPEC
for adding/changing the kind of diagnostics output, supporting
"text" and "sarif" output schemes.

This patch promotes the HTML output code from the test plugins so
that it is available from "-fdiagnostics-add-output=", using a
new "experimental-html" scheme, to allow simultaneous text, sarif
and html output, and to make it easier to experiment with.  The
patch adds Python-based testing of the emitted HTML.

The patch does not affect the generated HTML, which is still crude, and
not yet ready for end-users.  I hope to improve it in followups.

gcc/ChangeLog:
	PR other/116792
	* Makefile.in (OBJS-libcommon): Add diagnostic-format-html.o.
	* diagnostic-format-html.cc: Move here from
	testsuite/gcc.dg/plugin/diagnostic_plugin_xhtml_format.cc.
	Simplify includes.  Rename "xhtml" to "html" throughout.
	(write_escaped_text): Drop.
	(class xhtml_stream_output_format): Drop.
	(class html_file_output_format): Reimplement using
	diagnostic_output_file.
	(diagnostic_output_format_init_xhtml): Drop.
	(diagnostic_output_format_init_xhtml_stderr): Drop.
	(diagnostic_output_format_init_xhtml_file): Drop.
	(diagnostic_output_format_open_html_file): New.
	(make_html_sink): New.
	(xhtml_format_selftests): Convert to...
	(diagnostic_format_html_cc_tests): ...this.
	(plugin_is_GPL_compatible): Drop.
	(plugin_init): Drop.
	* diagnostic-format-html.h: New file.
	* doc/invoke.texi (-fdiagnostics-add-output=): Add
	"experimental-html" scheme.
	* opts-diagnostic.cc: Include "diagnostic-format-html.h".
	(class html_scheme_handler): New.
	(output_factory::output_factory): Add html_scheme_handler.
	(html_scheme_handler::make_sink): New.
	* selftest-run-tests.cc (selftest::run_tests): Call the new
	selftests.
	* selftest.h (selftest::diagnostic_format_html_cc_tests): New
	decl.

gcc/testsuite/ChangeLog:
	PR other/116792
	* gcc.dg/plugin/diagnostic_plugin_xhtml_format.cc: Move to
	gcc/diagnostic-format-html.cc.
	* gcc.dg/html-output/html-output.exp: New support script.
	* gcc.dg/html-output/missing-semicolon.c: New test.
	* gcc.dg/html-output/missing-semicolon.py: New test script.
	* gcc.dg/plugin/diagnostic-test-xhtml-1.c: Deleted test.
	* gcc.dg/plugin/plugin.exp (plugin_test_list): Drop moved plugin
	and its deleted test.
	* lib/gcc-dg.exp (load_lib): Add load_lib of scanhtml.exp.
	* lib/htmltest.py: New support script.
	* lib/scanhtml.exp: New support script, based on scansarif.exp.

libatomic/ChangeLog:
	PR other/116792
	* testsuite/lib/libatomic.exp: Add load_lib of scanhtml.exp.

libgomp/ChangeLog:
	PR other/116792
	* testsuite/lib/libgomp.exp: Add load_lib of scanhtml.exp.

libitm/ChangeLog:
	PR other/116792
	* testsuite/lib/libitm.exp: Add load_lib of scanhtml.exp.

libphobos/ChangeLog:
	PR other/116792
	* testsuite/lib/libphobos-dg.exp: Add load_lib of scanhtml.exp.

libvtv/ChangeLog:
	PR other/116792
	* testsuite/lib/libvtv-dg.exp: Add load_lib of scanhtml.exp.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>